'MRI Contrast Agents\r'

'â€Å"magnetic resonance imaging descent is used for a concoction of reasons.  Primarily, it is used to improve the detection of disease; that is, to maturation sensitivity and diagnostic confidence, to enhance the ability to part normal and aberrant tissue; and to identify the outcome of the disease” (Muroff, 2001).Contrast agentive roles ar chemical substances used in anatomical or functional mental imagery for the purport of increasing visual differences between normal and abnormal tissue.  These chemical substances argon used to alter laxation times.  Contrast agents ar classified by changes in relaxation times after injection.There be six important categories of MRI line of credit agents: GI, Intravenous, Intravascular ( origin pool), Tumor-specific, and Reticuloendothelial direct melodic phrase agents.Within the Gastrointestinal contrast agent category, there two subcategories: affirmatory and Negative contrast agents.Positive contrast agents cause a reduction in T1 relaxation times.  These agents appear brilliantly on images.  They may contain Manganese, Iron or Gadolinium as active elements.Positive contrast agents train three classifications: Para magnetic agents, short T1-relaxation agents, and a combine of the two.Paramagnetic contrast agents have magnetic centers which create magnetic fields.  These fields interact with water protons, and have a larger effect on relaxation rates.  They entangle ferric chloride and gadolinium, which cause T1 and T2 cut back.  In low concentrations, T1 trim holds the domination of the forcefulness of the call attention.  In gamy concentrations, T2 shortening causes the distinguish to decrease.  At mid-level concentration, T1 and T2 shortening show an make up in the signal on T1 weight images, and diminish the signal on T2 weighted images.Short T1-relaxation agents include mineral oil and oil emulsions.  In these agents, protons relax prompt than protons in water, which results in short T1 time.  In bowels with T1 weighted images, a bright signal is app atomic number 18nt.Combinations include emulsion oil that contains corn oil and ferric ammonium citrate, and an emusion containing baby formula with ferrous convert.  Combination contrast agents distribute evenly through the bowels.Negative contrast agents allow for appear largely dark on images.  They are frequently called superparamagnetic iron oxide (SPIO).  They have shorter T1 and T2 relaxation times.Negative contrast agents have three classifications: diamagnetic agents, superparamagnetic agents, and perfluorochemicals.One readily useable diamagnetic contrast agent is barium sulfate suspension.  It rationalises the loss of bowel signals, resulting in improved pancreatic visualization.Superparamagnetic contrast agents are generally administered orally.  They include magnelite ovalbumin microspheres and superparamagnetic iron oxide.  A large loss of the signal in the stomach and small bowels that give commodious visualization of the pancreas and anterior renal margins.  This contrast agent type â€Å"accumulates in the reticuloendothelial system of the liver-colored, and darkens healthy liver tissue in T2-weighted images” (mr-tip.com).Perfluorochemicals are organic compounds that interchange protons with fluorine.  They are a special group of electronegative contrast agents that appear completely dark on images, because they do not contain hydrogen atoms, which are responsible for the signal in MRIs.  In GI imaging, the purpose of perfluorochemicals is to give a complete signal absence in the bowels.Intravenous contrast agents include twain ionic and nonionic chelates.  When using paramagnetic metallic element ions as contrast agents, there is a high level of toxicity in the doses required for imaging.  Chelates reduce the chances of long term toxicity by reducing the toxic levels.Intravascular co ntrast agents remain in the blood longer than most other contrast agents.  They are highly useful in diagnosis imaging that may require longer imaging times.Tumor-Specific contrast agents are objectiveed to tumors.  There are four main types of tumor-specific agents:Metalloporphyrins target multiple types of tumors, such as melanomas and lymphomas.Monoclonal antibodies are for specific tumors such as colon carcinomas.Ferrioxamine is a paramagnetic agent used for the kidneys and urinary tract.Nitroxides are also paramagnetic agents, but are not astray used.Reticuloendothelial contrast agents are used in liver, spleen and lymph node MRIs.  In liver and spleen imaging, specific contrast agents are used that target the reticuloendothelial system of the liver and spleen.  Because of the inability of most imagers to disunite between normal and abnormal lymph nodes, USPIO has become widely used.  USPIO allows imagers to have the ability to differentiate between lymph nodes .â€Å"In cases where it is difficult to differentiate two types of tissue, because the signal chroma they produce is so similar, the solution is to add a contrast agent to one of them in rate to distinguish it from the other tissue” (GE healthcare, 2007).  MRI contrast agents affect hydrogen atoms and the time they take to tabulator to their original state, thereby increasing the signal intensity differences between the tissue with the contrast agent and the tissue without the contrast agent.  This results in an increase of contrasts on the image.ReferencesGE Healthcare (accessed January 13, 2007) www.amershamhealth.com/public/medical/mri_3.shtmlMedline Plus (revised March 2000) http://mplus.nlm.nih.gov/medlineplus/druginfo/uspdi/202770.htmlMR-Technology (accessed January 13, 2007) www.mr-tip.comMuroff, Lawrence R. (Aug. 2001) â€Å"MRI Contrast: Current Agents and Issues” Applied Radiology Online (vol. 30, no 8) www.appliedradiology.comRunge, Val M. (Aug. 2001) â€Å"The Safety of MR Contrast Media: A Literature canvas” Applied Radiology Online (Vol. 30, No. 8) www.appliedradiology.com\r\n'